Thermal-magnetic circuit breakers employ a pivotally-mounted bi-metal along with a pivotally-mounted magnetic armature to articulate the circuit breaker operating mechanism upon the occurrence of overcurrent conditions of predetermined magnitudes. When used within circuit breakers of increased ampere rating, corresponding larger thermal-magnetic trip units must be employed to safely respond to the increased steady state and overcurrent conditions.
U.S. Pat. No. 4,736,174 entitled "Molded Case Circuit Breaker Operating Mechanism" describes a common operating mechanism that is used over a wide range of ampere ratings for circuit breakers employing an electronic trip unit. The electronic trip unit provides an electrical signal to articulate the operating mechanism for separating the circuit breaker contacts. This allows the use of a rating plug which enables a single trip unit to be used over a wide range of circuit breaker ampere ratings.
The use of such electronic trip operating mechanisms within thermal-magnetic circuit breakers, would substantially reduce the inventory requirements with such thermal-magnetic trip units since a single operating mechanism would be used over a wide range of ampere ratings.
One example of a thermal-magnetic trip unit used within thermal-magnetic circuit breakers is found in U.S. Pat. No. 4,679,016 entitled "Interchangeable Mechanism for Molded Case Circuit Breaker". The thermal-magnetic trip unit provides complete circuit protection by responding to so-called "long-term" and "instantaneous" overcurrent conditions when used within an industrial-rated electrical distribution circuit.
U.S. Pat. No. 4,675,641 entitled "Rating Plug for Molded Case Circuit Breakers" describes a means for using a common thermal-magnetic trip unit such as described within the aforementioned U.S. Pat. No. 4,679,016 within a wide range of circuit breaker ampere ratings by the provision of thermally-variable rating plugs whereby the sensed circuit current through the thermal-magnetic trip unit remains within predetermined limits while the actual circuit current increases with increased ampere rating.
One purpose of the invention is to provide a trip accelerator in combination with the standard operating mechanism to render such operating mechanism usable with state-of-the-art thermal-magnetic trip units.